• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.297-306
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• 1999

In this research, the frost heave mechanism of the weathered tuff soil sampled from the area tying between Ulanbator and Beijing was studied. The frost heave tests were carried maintaining the constant temperature at both upper$(+5^{\circ}C)\; and\; lower(-5^{\circ}C)$ ends of the sample. Here, main emphasis is given on variation of the freezing point depression with the variation of applied overburden pressure. The expansion of ice lens and migration of the pore water towards freezing front were observed in the test. It was found that with the increase in overburden pressure there is decrease in heave rate and increase in the absolute value of a segregation-freezing temperature. Hence the equation between segregation-freezing temperature and overburden pressure could be suggested. Also the water content of the samples at the frozen side was shown to be higher than those at the unfrozen side. Similarly, the water at warmer part of the frozen tuff was found much higher than that of the cooler part.

• Journal of the Korean Geotechnical Society
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• v.19 no.1
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• pp.229-236
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• 2003

Ultrasonic propagation velocities of both the dilatational and shear waves through the weathered tuff soil sampled from the area tying between Ulanbator and Beijing were measured under temperature condition of near subzero by means of sing-around method. After comparing the results with obtained data on unfrozen water content, a linear relation between velocities and unfrozen water content was performed with high coefficient value. Experimental results of two kinds of rather uniform materials, namely, glass-beads and silica micro-beads, testified the similar linear relations. In addition, the change rate of dilatational wave velocities with the change of volumetric unfrozen water content was not dependent on soil type. Although a rational theory of the ultrasonic velocities dependence on the unfrozen water content is not yet proposed, the presented empirical relationships may suggest the appropriate evaluation to the effect of unfrozen water on dynamic characteristics of frozen soil.

• The Korean Journal of Quaternary Research
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• v.13 no.1
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• pp.35-43
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• 1999

Goryeri archaeological site is located in the upstream valley of the Danjang River. The basement rocks of the area are composed of the Cretaceous to Palaeogene biotite granite (KbGr), acidic dyke (Kad), Milyang Andesite (Kma) and Jyunggagsan Formation. Among them Milyang Andesite and Jyunggagsan Formation are prevailed in archaeological site and they are composed of reddish brown tuffaceous shale, sandstone and conglomerate, with intercalations of acidic tuffs and lapilli tuffs. The purpose of this research is not only to compare REE pattern of the soil-sedimentary deposits with those of surrounding rocks, but also to identify vitric tephra in the soil-sedimentary deposits derived from the andesite, acidic tuff and lapilii tuff, in order to illucidate the provenance of the vitric tephra. The rare earth element(REE) of the soils and sedimentary deposits results in the same REE pattern with those analyzed from the surrounding basement rocks. This indicates that the soils and sedimentary deposits are originated from the surrounding basement rocks, most probably from the andesite and lapilli tuff. In addition, vitric tephra were identified both in the Quaternary in-situ weathered soils and sedimentary deposits (PMU-13 and PMU-17), and in the weathered surrounding lapilli tuff. These vitric tephra are considered to be different from those of Japanese AT(Aira Tanzawa) -tephra. The latter is predominant with clean, platty, bubble-walled and Y-shaped vitrics, while the former is conspicuous with those shapes of large and diverse size and devitrified, as well as having secondarily bubbled-surfaces reflecting surface weathering. The size of vitric fragments in the Goryeri site is about 300${\mu}{\textrm}{m}$ and large in size in compasion to 150${\mu}{\textrm}{m}$ of Japanese AT-Tephra. The interim results of the research are contradictary to the explanations based on a series of AT-tephra researches carried by Japanese scholar. In short, the vitric materials of the Goryeri archaeological site are most probably originated from the weathering products of the surrounding basement rocks, and are different from the AT-tephra in their size, shape and devitrification properties. Thus it is highly recommended to have a further comprehensive research which is more emphasized the magmatic genesis of these vitric tephra in addition to the external shape and morphology.

• The Journal of Engineering Geology
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• v.10 no.2
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• pp.18-35
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• 2000

The most dominant type of landslide in Korea is debris flows which mostly take place along mountain slopes during the rainy season, July to August. The landslides have been reported to begin activation when rainfall is more than 200mm within 2days. The debris flows are usually followed by translational slips which occur upper part of mountain slopes and they transit to debris flow as getting down to the valleys. Lithology, location, slope inclination, grain size distribution of soil, permeability, dry density and porosity have been proved as triggering factor causing translational slides. The triggering data taken from mapping are statistically analysed to get landslide potential quantitatively. Rock mass creeps mostly occur on well bedded sedimentary rocks in Kyeongsang Basin. Although the displacement of rock mass creep is relatively small about 1m, the creep can cause severe hazards due to relatively large volume of the involved rock mass. Examples are rock mass creep occurred in the mouth of Hwangryongsan Tunnel, in Chilgok and in Sachon in 1999. Although the direct factor of the creeps are due to slope cutting at the foot area, more attention is required A rotational slide occurring within thick soil formation or weathered rock is also closely related to bottom part of slope cutting. It is propagated circular or semi-circular type. Especially in korea, the rotational slide may be frequently occurred in Tertiary tuff area. Because they are mainly composed of volcanic ash and pyroclastic materials, well developed joints and high degree of swelling and absorption can easily cause the slide. The landslide among the Pohang-Guryongpo national road is belong to this type of slide.